Ancillary filtering agent

ABSTRACT

The filter aid comprises finely divided plant fibers, which for a period of action have been subjected to a liquid treatment, which removes the sensorially active substances from the plant fibers.

[0001] The invention relates to a filter aid, as disclosed in thepreamble of claim 1, a proceess for its production and its application.

[0002] Cellulose-based filter aids have been known for a long time(“Ullmann's Encyklopädie der technischen Chemie”, 3rd edition (1951),first volume, page 492, key word “felted layers” and page 493, key word“filter aids”). Cellulose is produced in a multi-step chemical process,in which all sensorially active materials are removed from the rawmaterial.

[0003] Hence filter aids made of pure cellulose are used wherever thesensorial neutrality of the used filter aid is of great significance.Examples of cellulosic filter aids are EFC (low extract cellulose), finepowder cellulose, fine fibrillated cellulose, cationized powdercellulose, fine MCC (microcrystalline cellulose).

[0004] In contrast, filter aids made of untreated woodpulp are producedby mechanical comminution, thus only by physical treatment, and can,thus, release extractives (color, odor, flavor) during filtration.Therefore, the use of wood fiber-based filter aids is usually limited toindustrial filtrations, where relatively little demand is placed on thesensory analysis.

[0005] Not only for filtration in the food and luxury food sector, butalso for many industrial applications, they may not be considered, e.g.for sugar solutions (glucose, dextrose, fructose), molasses, dyesolutions, fats and oils and the like.

[0006] The difficult field of beverage filtration demands, on the onehand, complete sensorial neutrality of the used filter aid; on the otherhand, the number of commonly used filter aids are limited for economicreasons, since the maximum expense for the filter aid is fixed by theprice of the mineral filter aids dominating this market.

[0007] Usually beer filtration take place in two steps. The first stepusually involves a coarse filtration, during which operation the liquidusually passes through a precoated layer of a filter aid. This step isfrequently followed by a fine filtration (membrane, kieselguhr, etc.).

[0008] The standard filter aid for the precoat-type filter in thebeverage, especially beer, sector, is kieselguhr. A high percentage ofthe world beer production is clarified by kieselguhr filtration.Currently it exceeds more than 1.1 billion hl beer.

[0009] The total demand for filter aids is worldwide ca. 750,000 tonsper year, where inorganic materials, like, for example, kieselguhr,perlite or bentonite, constitute by far the largest share of thisamount. Of this total amount about 250,000 tons to 300,000 tons per yearare consumed worldwide by the beverage industry, largely by thebreweries, but also by producers of wine and fruit juices.

[0010] The amount of filter aids, which are based on organic rawmaterials that can regrow again (cellulose, woodpulp, etc.), is to dateonly ca. 20,000 tons per year, even though their use offers a pluralityof advantages over inorganic filter aids.

[0011] Thus organic filter aids are natural materials, whose qualityfluctuates only over a narrow range and whose occurrence can be renewedat regular intervals. In addition the use of organic filter aidspresents neither a health risk nor harmful effects for the environmentand nature. Pumps and conveying elements of the filtration system areprotected as much as possible owing to the nonabrasive property. Finallythe consumed filter cakes can be easily disposed, for example, throughland management, composting or animal fodder.

[0012] Of course, organic filter aids are in part many times moreexpensive than kieselguhr or they exhibit filtration properties that donot completely match those of kieselguhr.

[0013] For this reason organic filter aids have not been able to prevailto date against kieselguhr or are used in any case together withkieselguhr (report by J. Speckner “Cellulose as Filter Aids” in thejournal (“Brauwelt”, vol. 124 (1984), issue 46, pages 2058 to 2066, inparticular page 2062, left column top).

[0014] However, kieselguhr has become increasingly a problem. As anatural mineral material its occurrence is limited. Thus in the case ofkieselguhr one must resort more and more to low grade qualities in orderto meet the high demand of industry. The result is, however, a risingcost for the cleaning and processing of kieselguhr, which could in thelong run have a negative impact on its economic situation.

[0015] An even greater impact presents, however, the fact that theusers' attitude toward kieselguhr is becoming more critical.

[0016] This reservation stems from the problems posed to the lungs dueto many natural mineral materials and hence kieselguhr, a feature thatmust be taken very seriously from the point of view of occupationalmedicine. In 1988 the World Health Organization (WHO) categorizedkieselguhr as a carcinogenic substance following a series of animalexperiments. For handling there are strict regulations that are beingasserted and observed more and more in Germany.

[0017] Another factor is that the disposal of kieselguhr is becomingincreasingly more critical in industrial countries. A classification ashazardous waste makes landfilling considerably more difficult. With theintroduction of the new technical rules on municipal waste, the disposalsituation for kieselguhr is becoming more restrictive. In many casesdisposal of kieselguhr used as filter aid already gives rise to costs ofapproximately DM 600.00 per t of kieselguhr, when used in beerfiltration, or 1,500.00 per t of kieselguhr when used in the industrialfiltration of problematic substances.

[0018] Starting from these urgent problems in particular in the beerfiltration sector, the invention is based on the problem of developing afilter aid that is effective and can be provided economically.

[0019] This problem is solved by the invention described in claim 1.

[0020] Sensorially active substances, thus active with respect to color,odor and/or flavor, are to be removed from the filter aid to asufficient extent prior to use as a filter aid so that none of thesesubstances can pass into the filtrate to a significant extent and impairits sensorial properties. The particles are neutralized sufficiently toa certain extent sensorially in order to be able to serve as a filteraid. In so doing, it is essential that the treatment is carried out onlyto the extent that it is necessary for this purpose. The use of energyand chemicals remains in a justifiable range so that the product cancompete economically with kieselguhr. The action is, therefore, not asintensive as in the case of the production of cellulose from woodfibers. Surprisingly it has been found that by means of a liquidtreatment a sufficient neutralization of the particles with respect tosensorial aspects can be achieved without the need for simultaneouslyhigh pressures and temperatures to be employed, without the need forlarge amounts of aggressive chemicals and treatment periods of manyhours to days. In this respect the invention opens an expanded area ofapplication for plant fiber materials without the expense required forthe production of cellulose.

[0021] Although the starting point and preferred area of application forthe invention is beer and beverage filtration, which concerns theprovision of a kieselguhr substitute material, the invention is notrestricted to this area of application.

[0022] In a preferred embodiment of the inventive thought the particlescomprise wood particles (claim 2), for example, wood fibers (claim 3)or, in particular, wood comminution residues (claim 4), hence forexample sawdust, sanding dust, wood shavings, wood chips, cutting waste,chipped wood and the like.

[0023] However, cotton, straw, hemp, flax, bast, grasses are alsosuitable starting material, similarly cellulose-containing secondary rawmaterials, like old paper and paper waste.

[0024] In the preferred embodiment of the invention the particles havebeen treated with a dilute alkali solution (claim 5). However, treatmentwith diluted acid (claim 6), with an organic or inorganic solvent (claim7) or also only with water (claim 8) is not ruled out, where accordingto the kieselguhr is becoming increasingly more critical in industrialcountries. A classification as hazardous waste makes landfillingconsiderably more difficult. With the introduction of the new technicalrules on municipal waste, the disposal situation for kieselguhr isbecoming more restrictive. In many cases, disposal of kieselguhr used asfilter aid already gives rise to costs of approximately DM 600,000 per tof kieselguhr, if this was used in beer filtration, or 1500.00 per t ofkieselguhr if this was used in the industrial filtration of problematicsubstances.

[0025] Starting from these urgent problems in particular in the beerfiltration sector, the object underlying the invention is to develop afilter aid which is effective and can be provided economically.

[0026] This object is achieved by the invention described in claim 1.

[0027] Substances which are sensorially active, that is active withrespect to color, odor and/or flavor, are to be removed from the filteraid to a sufficient extent prior to use as filter aid, so that none ofthese substances can transfer into the filtrate to a significant extentand impair its sensory properties. The particles are neutralizedsufficiently to a certain extent sensorially in order to be able toserve as filter aid. It is essential here that the treatment is onlycarried out to the extent necessary for this purpose. The use of energyand chemicals remains in a justifiable range, so that the product cancompete economically with kieselguhr. The action is therefore not sointensive as is the case in the production of cellulose from woodfibers. Surprisingly, it has been found that by means of a liquidtreatment a sufficient neutralization of the particles with respect tosensory aspects can be achieved without the need for simultaneously highpressures and temperatures to be employed, large amounts of aggressivechemicals and treatment times of many hours to days. By means of theinvention, to a certain extent an expanded area of application is opento the wood particles, without this needing expenditure as in the caseof cellulose production.

[0028] Although the starting point and preferred area of application forthe invention is beer and beverage filtration, which concerns thecreation of a kieselguhr substitute material, the invention is notrestricted to this area of application.

[0029] Although DE 23 51 125 A1 discloses using, for the extraction ofmetals or metal ions from solutions, an adsorbent which is obtained bybringing, inter alia, wood sawdust into contact with a solution of ahydroxide of an alkali metal or alkaline earth metal, this is anadsorption, i.e. an accumulation of dissolved particles on the surfaceof the adsorbent, not a filtration, i.e. a separation from a suspension.

[0030] In the case of DE 41 10 252 C1, for prefloating a filter cake, amixture of filter aids of differing morphological and physicalproperties is used which comprise at least one component which increasesthe density of the filter cake and is made of high-density, chemicallyresistant metal and/or metal oxide and/or carbon particles of fibrousand/or granular structure and a further component of plastic fibersand/or cellulose fibers having a fiber length of from 1000 to 5000 μmand a fiber thickness of from 0.5 to 100 μm.

[0031] The wood particles of the filter aid according to the inventioncomprise, for example, wood fibers (claim 2) or, in particular, woodcomminution residues (claim 3), that is for example sawdust, sandingdust, wood shavings, wood chips, cutting waste, chipped wood and thelike.

[0032] The grinding performed in the production of the wood particles inthe invention substantially determines the filtration properties. Withfine grinding, the permeability of the filter layer is generally lower.By means of the grinding (micronization, fibrillation), in addition theparticle shape is affected which in turn changes the water value, whichis still to be explained, as a measure of the permeability of the filterlayer. In the case of fibrous cellulose products these can be fibrilatedto a greater or lesser extent. The grinding can also be performed in aplurality of steps in which a first grinding for the production of theparticles is followed by a further grinding after the treatment andbefore or after the drying.

[0033] The filter aid particles produced from wood particles are stillactually to have wood character, i.e. the lignin shall not have beenvirtually quantitatively extracted from the raw material wood, as occursin cellulose production in the sulfite or sulfate process by treatmentfor many hours at elevated pressure at temperatures far above 100° C.

[0034] The treatment time in the invention can be relatively short, forexample less than two hours, so that it is differentiated by one orderof magnitude from the treatment time in the production of cellulose. Thepurpose is the removal of only fractions of the wood which are unwantedwith respect to the use as filter aid, i.e. have an effect in terms offlavor, odor and/or color in the filtrate. This is not in this caseprimarily lignin, but compounds such as essential oils, terpeneoils andterpenoids, tannic acids, fats and waxes, phenolic substances (lignans,phenylpropanes, coumarin) stilbenes, flavonoids and the like, which makeup an amount of from approximately 4 to 5 percent by weight of the drywood. It has been found that these compounds can be, by means of atreatment with dilute alkali solutions acids [sic] even at roomtemperatures under atmospheric pressure, extracted from the wood or elsemade inactive to the extent that the treated wood particles aresufficiently neutral sensorially for the practical use as filter aid. Itis not the case that during a rigorous analysis no residues of theunwanted type can be observed any longer, but that, for example, amedium filtered using the filter aid does not permit, during sensorytesting, any wood flavor or wood aroma or any brown discoloration to berecognized. The treatment can be brief relative to the treatmentdurations of cellulose production.

[0035] An important feature in the treatment of the particles is, inaddition, that the treatment can also take place at temperatures below100° C. and simultaneously at atmospheric pressure, which substantiallysimplifies the plant required for producing the filter aid.

[0036] The filter aid of the invention can be prepared particularlyeconomically. The costs may be in the same order of magnitude as thecosts of kieselguhr, but only about one third of the costs for cellulosepowder.

[0037] It also appears to be the case that the particles treatedaccording to the invention have on the surface an additionally roughenedor fissured structure which advantageously affects the filterproperties.

[0038] Underlying the preamble of claim 1 is French Patent 385 035 whichhas, as its subject matter, wood fibers used for filter purposes whichare treated, to avoid rotting, with a permanganate solution with orwithout addition of acid.

[0039] From JP-A 73 28 353, DE 41 10 252 C1 and EP 747 104 A2 can betaken the use of cellulose fibers, that is not alkali-solution-treatedwood particles, mixed with other components as filter aid.

[0040] From FR 534 288 there arises a filter aid for wines, which aidconsists of wood wool which is thoroughly washed and treated with 1%strength tartaric acid.

[0041] According to claim 4 the filter aid can comprise essentially onlywood particles of one and the same type, size and pretreatment, that iscan essentially be uniformly composed.

[0042] However, it is also possible according to claim 5 for the filteraid to comprise at least two particle fractions comminuted according todifferent processes, in order to be able to set the filtrationproperties in accordance with the requirements.

[0043] From the same aspect, the filter aid can comprise at least twoparticle fractions comminuted to different dimensions (claim 6) and/orat least two particles produced from different starting materials (claim7).

[0044] The filter aid can also comprise other fractions which do notaffect the filtration properties (claim 8).

[0045] It can also be a mixture with other filter-active constituents,i.e. not consisting of plant fibers (claim 9), also with mineralconstituents (claim 10), namely with kieselguhr (claim 11), which wouldhave the effect of reducing the kieselguhr content and the associatedproblems mentioned at the outset.

[0046] However, suitable additional constituents are also other mineralfilter aids, in particular perlite (claim 12).

[0047] According to claim 13, the largest mean particle diameter of theready-to-use filter aid shall be less than 3.0 mm.

[0048] In contrast, in the case of fibrous particles, the mean fiberdiameter shall be less than 1.0 mm (claim 14).

[0049] Since the particles are produced by grinding, they do not have anexact size, but a size distribution for instance according to a Gaussiancurve. The position of the maximum of this curve may be taken to meanhere the highest particle dimension.

[0050] The filter aid of the invention can be used to form prefloatfilter layers in the same manner as was previously the case with mineralfilter aids.

[0051] The invention also extends to a process according to claim 15 forpreparing the filter aid in which the particles are digested by thetreatment liquid in the course of a period of action.

[0052] A suitable temperature range in the treatment of the particles isthe range of room temperature, which, although it requires no heatingenergy consumption, does require longer treatment times (claim 16).

[0053] A further practicable region with shorter treatment times is50-100° C. (claim 17).

[0054] According to claim 18, atmospheric pressure in the temperaturerange of 70 to 90° C. can be employed, which is a temperature markedlyincreased with respect to room temperature, but is below the boilingpoint and eliminates the use of pressure vessels. This leads to a usablefilter aid with a minimum of equipment and energy consumption.

[0055] “Dilute alkali solution” shall mean an aqueous solution having acontent of from 2 to 10% by weight of the dry alkali, based on thesolids content (claim 19).

[0056] In the preferred embodiment of the invention, sodium hydroxidesolution is used (claim 20).

[0057] The period of action depends, apart from the pressure andtemperature, on the solution capacity of the dilute alkali solution forthe unwanted constituents. In the case of dilute alkali solution, it isalso the case that it is not periods of action in the seconds regionwhich come into question, but those which are short in comparison withthe periods of action of many hours to days necessary in celluloseproduction. The period of action is partly dependent on the particlesize.

[0058] It is, moreover, of a size determined by the fact that preciselyonly the sensory-critical substances are to be removed from theparticles, in particular the wood particles. The latter purpose isachieved when at most 10% by weight on an absolutely dry basis of thewood constituents are removed (claim 21), whereas the production ofcellulose relates to the liberation of generally more than 30% of thewood constituents.

[0059] The period of action can be, with an alkali solution treatment,in particular between 5 and 120 min. (claim 22).

[0060] The consistency, i.e. the proportion by weight of the particlesin the dilute alkali solution, can be from 5 to 25% in the treatment(claim 23).

[0061] The particles, after the period of action, can be washed anddried (claim 24).

[0062] The particle size (maximum of the particle size distribution) canbe up to 10 mm, preferably 0.1 to 1.0 mm, during the treatment (claim25).

[0063] Since a grinding in the wet phase changes the particle shape, apossibility is opened up in this manner of setting the water value(claim 26).

[0064] In individual cases it is possible, without relinquishing thelack of sensory hazard to further comminute the particles after thealkali solution treatment and the drying, simultaneously with the dryingor after the drying (claim 27).

[0065] To obtain clear conditions with respect to the filter properties,it is advisable according to claim 28 to classify the particles afterthe alkali solution treatment and the drying.

[0066] The invention is also embodied in the use of finely divided woodparticles which have been subjected to a treatment with a dilute lute[sic] at a temperature below 100° C. and at atmospheric pressure, whichtreatment removes the sensorially active substances from the woodparticles, as filter aid (claim 29), in particular when the particleshave been treated according to the process of claims 15 to 28 (claim30).

[0067] A suitable use is in particular in beverage filtration, inparticular beer filtration (claim 31).

[0068] Other fields of application of the invention are food filtration(claim 32), for example sugar solutions, edible oil, fat, gelatin,citric acid, alginate etc., filtration in the chemical sector (claim33), for example chloralkali, in the sector of the cleaning of auxiliaryliquids in metalworking (claim 34), for example cutting fluids, rollingoils, polishing oils, etc., and in the pharmaceutical and cosmeticssector (claim 35).

[0069] To study the efficacy of the novel treatment of the plant fiberparticles, untreated plant fiber particles (Lignocel C 120) werecompared with plant fiber particles treated according to the invention(Sample No. 1; Sample No. 2; Sample No. 3). The Samples No. 1 to No. 3were treated as follows:

[0070] Sample 1:

[0071] To produce the treated plant fiber particles, 330 g of wood fiberflour (particle range: 70-150 πm), 3700 ml of water and 15.8 g of solidsodium hydroxide were digested (reacted) in a mixing and treatmentreactor at from 20° C. to 25° C. without additional heating and withoutstirring. The solids content was below 10% by weight, the retention timewas at least 16 hours, the pH of the aqueous alkali solution was below11.3 after 16 hours.

[0072] The sodium hydroxide solution was filtered off by vacuum via aplastic filter, the predried wet cake was slurried in hot water (70°C.), so that a solids content below 15% by weight was achieved. A finalpH of from 3.0 to 7.0 was set using dilute hydrochloric acid and thesolution was filtered off under vacuum via a plastic filter. Thesubsequent rinsing was performed at least twice each time with 200 to500 ml of water at 70° C.

[0073] Sample 2 was treated with hot alkali solution and rinsed cold. Ina mixing and treatment reactor, at temperatures above 50° C. and withstirring 330 g of wood fiber flour (particle range: 70-150 μm), 3700 mlof water and less than

1. Filter aid which comprises finely divided wood particles which havebeen subjected to a chemical liquid treatment, characterized in that theparticles have been subjected to a treatment with a dilute alkalisolution at a temperature below 100° C. and at atmospheric pressure,which removes the sensorially active substances from the wood particles.2. Filter aids according to claim 1, characterized in that the particlescomprise wood fibers.
 3. Filter aids according to claim 1, characterizedin that the particles comprise wood comminution residues.
 4. Filter aidaccording to one of claims 1 to 3, characterized in that it essentiallycomprises only wood particles of one and the same type, sizedistribution and pretreatment.
 5. Filter aid according to one of claims1 to 3, characterized in that it comprises at least two fractions ofparticles comminuted by different processes.
 6. Filter aid according toone of claims 1 to 5, characterized in that it comprises at least twofractions of particles comminuted to different dimensions.
 7. Filter aidaccording to one of claims 1 to 6, characterized in that it comprisesfractions of particles produced from at least two different startingmaterials.
 8. Filter aid according to one of claims 1 to 7,characterized in that it comprises other organic or inorganic fractionswhich do not affect the filtration properties.
 9. Filter aid accordingto one of claims 1 to 8, characterized in that it comprises otherfilter-active fractions.
 10. Filter aid according to one of claims 1 to9 characterized in that it comprises other mineral fractions.
 11. Filteraid according to one of claims 1 to 10, characterized in that itcomprises kieselguhr.
 12. Filter aid according to one of claims 1 to 11,characterized in that it comprises perlite.
 13. Filter aid according toone of claims 1 to 12, characterized in that the mean particle dimensionof the ready-to-use filter aid is below 3.0 mm.
 14. Filter aid accordingto one of claims 1 to 13, characterized in that the mean fiber diameteris below 1.0 mm in the case of fibrous particles.
 15. Process forproducing the filter aid according to one of claims 1 to 14,characterized in that the particles are digested with the dilute alkalisolution during a period of action.
 16. Process according to claim 15,characterized in that the temperature of the dilute alkali solutionduring the treatment is in the range of room temperature.
 17. Processaccording to claim 15 or 16, characterized in that the temperature ofthe dilute alkali solution during treatment is 50-100° C.
 18. Processaccording to one of claims 15 to 17, characterized in that thetemperature of the dilute alkali solution during the treatment is from70 to 90° C.
 19. Process according to one of claims 15 to 18,characterized in that concentration of the dilute alkali solution isfrom 2 to 10% by weight, based on the solids content.
 20. Processaccording to one of claims 15 to 19, characterized in that the alkalisolution used is sodium hydroxide solution.
 21. Process according to oneof claims 15 to 20, characterized in that the period of action is of aduration such that at most 10% by weight on an absolutely dry basis ofthe wood constituents are removed.
 22. Process according to one ofclaims 15 to 21, characterized in that the period of action is from 5 to120 min.
 23. Process according to one of claims 15 to 22, characterizedin that the consistency during the treatment is from 5 to 25%. 24.Process according to one of claims 15 to 23, characterized in that theparticles are washed and dried after the period of action.
 25. Processaccording to one of claims 15 to 24, characterized in that the particlesize during the treatment is up to 10 mm, preferably from 0.1 to 1.0 mm.26. Process according to one of claims 15 to 25, characterized in thatthe water value is set by influencing the grinding in the wet phase(refiner).
 27. Process according to one of claims 15 to 26,characterized in that the particles are further comminuted after thetreatment and before the drying, simultaneously with the drying or afterthe drying.
 28. Process according to one of claims 15 to 27,characterized in that the particles are classified after the treatmentand the drying.
 29. The use of finely divided wood particles which havebeen subjected to a treatment with a dilute alkali solution at atemperature below 100° C. and at atmospheric pressure, which treatmentremoves the sensorially active substances from the wood particles, asfilter aid.
 30. The use of finely divided wood particles which have beentreated according to one of claims 15 to 28 as filter aid.
 31. The useaccording to claim 29 or 30 in beverage filtration, in particular beerfiltration.
 32. The use according to claim 29 or 30 in food filtration.33. The use according to claim 29 or 30 in the sector of the cleaning ofliquids in the chemicals industry.
 34. The use according to claim 29 or30 in the sector of the cleaning of auxiliary liquids in metalworking.35. The use according to claim 29 or 30 in the sector of pharmaceuticalsand cosmetics.